Has my instance of Ubuntu been overwritten?

I [Lenovo Thinkpad P15s, Ubuntu 20.04 pre-installed] was in mood for adventure and tried live version of another OS, but booting the live disk ended into GRUB mode (tried making the live disk multiple times, and every time it ended up this way). The adrenaline rush from my previous adventure (resizing my root partition using boot-able version of GParted) persuaded me to set the root and prefix in the GRUB mode, and I ended up booting into the Ubuntu OEM mode, which prompted me to setup a new user.

Frozen in my tracks, I hurriedly rebooted the system, unplugged the live disk, and hoped for it to boot into my original account, and things didn't change. I ended up creating a new user, and thankfully, the partitions were still intact and all the files were there. I tried su -l [original user name], but it didn't recognise the user name. I installed the boot-repair utility, and the situation persisted. So I have turned to you, my fellow Ubuntu adventurers; please help me login into my original user account.

I have added the initial section of the boot-repair's report below, and you can find the full report here. TIA.

boot-repair-4ppa203                                              [20230130_1238]

============================== Boot Info Summary ===============================

 => No boot loader is installed in the MBR of /dev/nvme0n1.

nvme0n1p1: _____________________________________________________________________

    File system:       vfat
    Boot sector type:  FAT32
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  
    Boot files:        /efi/BOOT/bkpbootx64.efi /efi/BOOT/bootx64.efi 
                       /efi/BOOT/fbx64.efi /efi/BOOT/mmx64.efi 
                       /efi/ubuntu/grubx64.efi /efi/ubuntu/mmx64.efi 
                       /efi/ubuntu/shimx64.efi /efi/ubuntu/grub.cfg

nvme0n1p2: _____________________________________________________________________

    File system:       vfat
    Boot sector type:  FAT32
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  
    Boot files:        /boot/grub/grub.cfg /efi/boot/grubx64.efi 
                       /efi/boot/shimx64.efi

nvme0n1p3: _____________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info: 
    Operating System:  Ubuntu 20.04 LTS
    Boot files:        /boot/grub/grub.cfg /etc/fstab /etc/default/grub

nvme0n1p4: _____________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info: 
    Operating System:  
    Boot files:        


================================ 1 OS detected =================================

OS#1:   Ubuntu 20.04 LTS on nvme0n1p3

================================ Host/Hardware =================================

CPU architecture: 64-bit
Video: UHD Graphics GP108GLM [Quadro P520] from Intel Corporation NVIDIA Corporation
BOOT_IMAGE of the installed session in use:
/boot/vmlinuz-5.6.0-1020-oem root=UUID=ca94ce09-54a0-4ffc-818a-82eb0fda89e0 ro quiet splash vt.handoff=7
df -Th / : /dev/nvme0n1p3 ext4  169G  7.8G  153G   5% /

===================================== UEFI =====================================

BIOS/UEFI firmware: N2XET29W (1.19 ) from LENOVO
The firmware is EFI-compatible, and is set in EFI-mode for this installed-session.
SecureBoot disabled (confirmed by mokutil).

blkid (filtered): ______________________________________________________________
 
NAME        FSTYPE   UUID                                 PARTUUID                             LABEL      PARTLABEL
nvme0n1                                                                                                   
├─nvme0n1p1 vfat     17FD-043C                            59c695de-6561-4b4c-a034-6dcd3b2ab965 EFI System EFI
├─nvme0n1p2 vfat     1808-AC6D                            1e7cf269-1375-421a-adae-f82762da27ee PQSERVICE  Recovery Partition
├─nvme0n1p3 ext4     ca94ce09-54a0-4ffc-818a-82eb0fda89e0 20d2de9f-ecdd-4dac-84df-db17b172ca14            
└─nvme0n1p4 ext4     139b4dc4-7332-46e8-99f1-8433cbbbc860 5c372a5f-93df-4771-b1b0-4c83ab46269c            
 
Mount points (filtered): _______________________________________________________
 
                Avail Use% Mounted on
/dev/nvme0n1p2   1.3G  66% /mnt/boot-sav/nvme0n1p2
/dev/nvme0n1p3 152.5G   5% /
/dev/nvme0n1p4 200.7G  27% /mnt/boot-sav/nvme0n1p4

Update1: The nvme0n1p4 partition, which was previously where I mount /home, is now an external media which is not used by the OS. The OS which is now loaded looks like the factory version that came along, and I had to install all the softwares again, even though the root partition in both my instances are same.

So, I tried mounting the nvme0n1p4 as the root partition, and added UUID=139b4dc4-7332-46e8-99f1-8433cbbbc860 /home ext4 errors=errors=remount-ro 0 1 to /etc/fstab, and rebooted the system. It failed to recognise the partition as the /home and failed to open any application except the terminal.

Update2: I tried rEFInd to see if it actually picks up my original instance of Ubuntu, and it did find two different options with Ubuntu symbol, but both of them booted into the new instance of Ubuntu installed.